The goal of search is to find the most relevant information. Popular search engines such as Yahoo!, Google, and MSN, have relied on traditional horizontal approach to searching. Horizontal search engines are usually characterized by a lack of a hierarchal structure. Horizontal search engines rely on search crawlers that typically index almost everything over the internet or a network. The results they produce span a very broad range of categories. However, users frequently desire search results from a narrower range of categories.
Since search queries tend to be short, one technique would require the search query to be more complex. Some search systems allow users to input complex logic queries in order to get better results. This approach is undesirable because the required search format in such systems is no longer intuitive. Some users would therefore not take the time to learn to use a system and avoid it altogether. Also it takes more time and effort for one familiar with the particular search format to craft a proper search statement. There are other search engines that give more relevant results to a particular topic, but this is because the search engine indexes and works for one domain. Hence, there is a need for a robust, practical approach to narrow search results to user desired topic domains while allowing search queries to remain simple and brief.